1. Field of the Invention
The present invention relates generally to an engine, and more particularly to improvements in an internal combustion engine with dry sump lubricating system.
2. Description of the Related Art
Internal combustion engines with dry sump lubricating system are known in which a feed pump supplies lubricating oil from a lubricating oil tank disposed outside an engine body to all moving parts in the engine, and the oil which had dropped down into a crank chamber after circulating through the engine is immediately picked up from the crank chamber and sent back into the lubricating oil tank by means of a return pump.
One example of such engines is disclosed in Japanese Patent Laid-open Publication No. SHO 62-23514, which includes a generally L-shaped lubricating oil tank attached to one side of an engine body extending in the longitudinal direction of a crankshaft, and a single feed pump and two return pumps all driven by rotation of the crankshaft and disposed in a space defined between the engine body and the L-shaped lubricating oil tank. The feed pump has an oil pickup tube extending into the lubricating oil tank and picks lubricating oil up from the lubricating oil tank through the oil pickup tube and supplies the lubricating oil through oil passages to moving parts in the engine. After circulating through the engine, the lubricating oil drops down into a crank chamber and is collected into a pair of parallel oil sumps extending in a bottom surface of the crank chamber in a longitudinal direction of the crankshaft. Each of the return pumps sends the lubricating oil from a corresponding one of the oil sumps back into the lubricating oil tank through one recovery passage. Baffle plates are provided above the oil sump so that the lubricating oil in the oil sump is prevented from splashing over the crankshaft. A breather device is provided at an upper end of the lubricating oil tank to interconnect an internal space of the lubricating oil tank and an intake device of the engine for circulating oil vapors into an intake system of the engine.
The disclosed engine has the advantage of having oil passages of reduced lengths, however, it still has a drawback that the lubricating oil tank attached to the side of the engine body increases the engine width (i.e., extent of the engine in a transverse direction of the crankshaft), posing a great spatial limitation when the engine is installed in a motor vehicle or a small boat. Additionally, since the baffle plates are each comprised of a single press-formed rectangular plate extending over and along the entire length of the oil sump, production of such baffle plates requires use of a press-forming mold assembly which is relatively large in size and expensive to manufacture and hence increases the manufacturing cost of the engine. Furthermore, when the engine is greatly inclined from the vertical or turned upside down, the breather device provided at the upper end of the lubricating oil tank may allow the lubricating oil to flow out from the lubricating oil tank and then enter the intake system of the engine. Inflowing of the lubricating oil may deteriorate the engine performance and sometimes cause a malfunction of the engine. The known engine is, therefore, not suitable for use in a small boat such as a closed lifeboat which while in use is subjected to great changes in posture including overturn or capsize.
Another example of the known engines with dry sump lubricating system is disclosed in Japanese Patent Laid-open Publication No. HEI 3-9027. The disclosed engine is an automotive engine and includes a lubricating oil tank secured to a bottom wall of the crankcase of an engine body, a supply pump and two return pumps, all the pumps being driven by a power take-out shaft extending parallel to a crankshaft. The feed pump picks up lubricating oil from the lubricating oil tank using an oil pickup tube extending into the lubricating oil tank and supplies the lubricating oil to moving parts in the engine. After circulating through the engine, the lubricating oil drops down into the crankcase and gathers into an elongated groove-like oil sump extending in the bottom surface of a crank chamber in the longitudinal direction of the crankshaft. Each of the return pumps returns the lubricating oil from the oil sump to the lubricating oil tank through a recovery passage connected to each end of the oil sump. A breather device is built in an upper portion of the lubricating oil tank. The lubricating oil tank faces in the forward direction of the motor vehicle to provide an improved cooling efficiency of the lubricating oil held in the lubricating oil tank. To this end, the crankshaft is arranged in a transverse direction of the vehicle, cylinders are inclined from the vertical toward the backward direction of the vehicle, and the power take-out shaft is disposed in a diagonal upward position of the crankshaft such that an acute angle is defied between a plane extending between an axis of the power take-out shaft and an axis of the crankshaft and a plane in which axes of the cylinders lie.
Since the engine body and the lubricating oil tank are inclined in opposite directions with respect to the axis of the crankshaft, the overall height of the known engine is relatively small. The known engine, however, has a large width (an extent of the engine in the transverse direction of the crankshaft) which may pose a great spatial limitation when the engine is installed in the vehicle. Another drawback is that when the engine is subjected to a great change in posture such as overturn, the lubricating oil may flow out from the lubricating oil tank through the breather device and then enter an intake system of the engine. The lubricating oil thus introduced may deteriorate engine performance and sometimes cause a malfunction of the engine. The known engine is not suitable for use in a small boat such as a closed lifeboat which, in use, is subjected to great changes in posture including overturn.
An engine suitable for use in a small boat such as a closed lifeboat involving great changes in posture during use is disclosed in Japanese Utility Model Publication No. SHO 60-8109. The disclosed engine has a lubricating system which includes an oil tank provided separately from an oil pan of the engine for receiving therein lubricating oil from the oil pan when the engine is rolled from the upright position through an angle of more than 45 degrees, an oil pipe branched from an oil passage at the engine side and projecting into the oil tank, and a valve assembled in the oil pipe and adapted to open when the engine rolling angle is more than 40 degrees. A breather device of the engine includes a mist separating chamber which communicates with a crank chamber of the engine through a breather of an engine body and a breather pipe. The mist separating chamber is disposed adjacent the oil tank and communicates with the oil tank through a small opening or orifice. A mist pipe, which is connected by a connecting pipe to an intake manifold, projects into the mist separating chamber.
When the rolling angle of the engine is smaller than 45 degrees, a lubricating pump driven by the engine sends the lubricating oil from the oil pan to a main gallery through a branched portion of the oil passage. In this instance, since the valve is in the closed position, the oil pipe does not function as an oil pickup pipe of the lubricating pump. Accordingly, after circulating through the engine, the lubricating oil drops back down into the oil pan.
When the engine rolling angle exceeds 45 degrees, the lubricating oil in the oil pan flows by gravity down into the oil tank through the breather of engine body and the breather pipe. In this instance, the valve assembled in the oil pipe is opened to thereby enable the oil pipe to function as an oil pickup pipe of the pump. As a result, the lubricating oil is picked up from the oil tank through the oil pipe and supplied to the engine side. Since the oil tank and the mist separating chamber communicate with each other through the orifice, a small amount of lubricating oil may flow from the oil tank through the orifice into the mist separating chamber depending on the rolling angle of the engine. However, due to an inlet of the mist pipe being disposed so as not to be flooded with the lubricating oil coming into the mist separating chamber, the lubricating oil is prevented from flowing into the intake manifold through the mist pipe and the connecting pipe.
Although the conventional engine lubricating system has an oil tank provided separately from the crank chamber, it does not belong to the dry sump lubricating system due to the presence of the oil pan of a size which must be large enough to hold substantially all the lubricating oil being used. The large oil pan increases the overall height of the engine. Additionally, since the lubricating oil is caused to flow by gravity down into the oil tank when the engine rolling angle exceeds 45 degrees, the oil tank should preferably be disposed above the upper end of a head cover to secure more recovery of the lubricating oil in the oil tank particularly when the engine is turned upside down. Thus, no reduction in height of the conventional engine is expected.